[clangd] Remove the whitelist std symbols in CanonicalIncludes.

[hokein]

Summary

These symbols have been included via StdSymbolMap.inc.

[hokein]

Remove more symbols.

clangd/index/CanonicalIncludes.cpp

collectIWYUHeaderMaps(CanonicalIncludes *Includes) {
 
   private:
     CanonicalIncludes *const Includes;
   };
   return llvm::make_unique<PragmaCommentHandler>(Includes);
 }
 
 void addSystemHeadersMapping(CanonicalIncludes *Includes) {
-  static const std::vector<std::pair<const char *, const char *>> SymbolMap = {
-      // Map symbols in <iosfwd> to their preferred includes.
-      {"std::basic_filebuf", "<fstream>"},
-      {"std::filebuf", "<fstream>"},
-      {"std::wfilebuf", "<fstream>"},
-      {"std::basic_istream", "<istream>"},
-      {"std::istream", "<istream>"},
-      {"std::wistream", "<istream>"},
-      {"std::basic_ostream", "<ostream>"},
-      {"std::ostream", "<ostream>"},
-      {"std::wostream", "<ostream>"},
-      {"std::uint_least16_t", "<cstdint>"}, // <type_traits> redeclares these
-      {"std::uint_least32_t", "<cstdint>"},
 #define SYMBOL(Name, NameSpace, Header) { #NameSpace#Name, #Header },
       #include "StdSymbolMap.inc"
 #undef SYMBOL
   };
-  for (const auto &Pair : SymbolMap)
-    Includes->addSymbolMapping(Pair.first, Pair.second);
 
   // FIXME: remove the std header mapping once we support ambiguous symbols, now
   // it serves as a fallback to disambiguate:
   //   - symbols with mulitiple headers (e.g. std::move)
-  //   - symbols with a primary template in one header and a specialization in
-  //     another (std::abs)
   static const std::vector<std::pair<const char *, const char *>>
       SystemHeaderMap = {
           {"include/__stddef_max_align_t.h", "<cstddef>"},
           {"include/__wmmintrin_aes.h", "<wmmintrin.h>"},
           {"include/__wmmintrin_pclmul.h", "<wmmintrin.h>"},
           {"include/adxintrin.h", "<immintrin.h>"},
           {"include/ammintrin.h", "<ammintrin.h>"},
           {"include/avx2intrin.h", "<immintrin.h>"},